Internal combustion engines commonly employ a vibration damper affixed to the front end of the crankshaft to absorb and dissipate torsional crankshaft vibrations during engine operation. Such crankshaft vibration dampers consist of a central hub keyed to the crankshaft exteriorly of the engine block having a circular periphery. An annular metal inertia ring circumferentially surrounds the hub periphery in radially spaced relationship thereto and the annular cavity between the hub and the inertia ring is filled with a vibration damping elastomer, usually rubber. The elastomer maintains the assembly of the inertia ring on the hub, and in some vibration damper constructions this assembly is created by friction forces by producing a stressing of the elastomer during assembly between the hub and inertia ring wherein the elastomer is "compressed" therebetween.
Also, in addition to prestressing the elastomeric material as it is introduced into the annular cavity between the hub and inertia ring, adhesive may be utilized to augment the assembly between the components. Such adhesives may be of the thermosetting type wherein heating of the vibration damper after assembly is required to heat the adhesive to a bonding temperature.
A conventional manner for assembling internal combustion engine crankshaft vibration dampers of the above type consists of the following steps:
A thermosetting adhesive is applied to the circumference of the hub flange and the inner surface of the inertia ring. These components are then placed within a jig in concentric relationship which defines an annular concentric cavity between the surfaces to which the adhesive has been applied.
An elongated strip of elastomeric material, usually rubber, is formed into a ring and is placed within the jig and is axially forced into the annular cavity between the hub and inertia ring. As the radial thickness of the rubber ring is slightly greater than the radial thickness of the cavity receiving the ring, the elastomer is prestressed (stretched), and tends to expand to its normal dimensions, but is confined by the hub and inertia ring producing frictional forces between the elastomer and the hub and inertia ring. These frictional forces will produce an initial mechanical assembly of the damper components.
The assembled damper is then removed from the assembly jig and placed upon a gage which is rotatable and "run out", i.e. possible eccentricity of the inertia ring relative to the hub is checked to assure that the inertia ring concentricity is within the acceptable tolerances.
The assembled damper is then placed within portable clamps which engage both the hub and inertia ring to prevent axial displacement therebetween. A plurality of clamped vibration dampers are placed upon a rack, and the rack includes spaced layers wherein air flow between adjacent dampers is permitted.
The rack of clamped dampers is then placed within a gas-fired convection oven wherein heat is circulated and the entire rack, vibration dampers and clamps are heated to approximately 300.degree. F. Difficulty is often encountered in obtaining uniform temperature within the convection oven, and the rack is usually retained in the oven to assure that all of the vibration dampers achieve a temperature sufficient to bond the adhesive, which is approximately 250.degree. F.
After heating, the rack is removed from the oven and allowed to cool to room temperature. Several hours are required to achieve such cooling.
After cooling, the vibration dampers are individually unclamped, and bonding of the adhesive to the elastomeric material, hub and inertia ring will have taken place.
The vibration dampers are again placed upon a rotatable gage and run out or concentricity checked. Thereafter, timing marks are embossed on the inertia ring and the damper is placed upon a rotating balancer, and balanced, and the balanced dampers are then boxed for shipment.
The aforedescribed method of bonding crankshaft vibration dampers is inefficient in that the individual clamping of the dampers, and unclamping, is time consuming. Additionally, as the convection oven heating system requires that the oven, rack, clamps and vibration dampers all be heated to a bonding temperature, energy is inefficiently utilized as the heat is only necessary to bond the adhesive, and the energy required to heat the oven, rack, clamps and portions of the hub and inertia ring remote from the elastomeric ring serves no purpose, and is wasted.
Further, the aforedescribed method utilizing the convection oven exposes the elastomer to a bonding temperature for a considerable length of time, and the effect of such heat on the elastomer over such duration accelerates "aging" of the elastomer and has a deleterious effect thereon.
Also, because of the heating of the entire assembly of the vibration damper, and clamps, concentricity between the inertia ring and the hub may vary before and after heating, and the two gaging operations are necessary to assure concentricity and quality of assembly.
In the practice of the invention heating of the thermosetting adhesive is now accomplished by low frequency electrical induction, and as described below, the use of electrical induction heating simplifies the assembly of vibration dampers for engine crankshafts. It is appreciated that induction heating has previously been utilized in the assembly of components utilizing adhesives, and typical disclosures of such induction heating systems are shown in U.S. Pat. Nos. 3,740,512; 3,798,403 and 4,128,449. However, such prior disclosures are not directed to the use of induction heating in the assembly of engine vibration dampers and do not suggest the advantages arising from the use of induction heating in the manufacture of crankshaft vibration dampers.
It is an object of the invention to provide a system for assembling internal engine crankshaft vibration dampers utilizing a thermosetting adhesive wherein electrical induction heating is employed to produce the adhesive bonding temperatures.
Another object of the invention is to provide a process for assembling crankshaft vibration dampers including an elastomer bonded to metal components wherein heating of a thermosetting adhesive is accomplished without adversely affecting the physical characteristics of the elastomer.
Yet a further object of the invention is to provide a system for assembling engine crankshaft vibration dampers utilizing an elastomer and a thermosetting adhesive wherein the steps of manufacture are simplified with respect to previous assembly procedures and wherein accuracy of assembly is maintained.
In the practice of the invention the vibration damper hub, inertia ring and elastomeric ring are assembled as previously described wherein the prestressing of the rubber ring will frictionally maintain the assembly of the components prior to bonding. The assembled damper is then placed upon a rotatable gage so that run out, i.e. concentricity of the inertia ring, may be checked. Thereafter, timing marks are stamped upon the damper, usually the inertia ring, and the damper is placed upon a rotatable balancer, and balanced. It will be appreciated that all of the aforementioned steps have taken place prior to bonding of the thermosetting adhesive initially applied to the hub and inertia ring surfaces engaging the elastomeric ring in contrast to the bonding procedure using the convection oven.
Thereupon, the balanced damper assembly is placed within electrical induction heating apparatus and the hub and inertia ring are firmly clamped therein to prevent relative axial displacement therebetween. Clearance is provided adjacent the ends of the elastomeric material whereby thermal expansion of the elastomer may occur during heating.
The clamped damper is then exposed to low-frequency high-alternating current electrical energy as generated by a water-cooled coil located below the damper. The coil is of such configuration that the resultant heating occurs primarily in the hub flange and in the inertia ring adjacent the elastomeric ring, and the current flow is continued for a duration, approximately one half minute, sufficient to heat the hub flange surface coated with the adhesive and the adhesive-coated inertia ring surface to a temperature sufficient to bond the adhesive to these surfaces and the elastomeric ring.
After heating, the damper is removed from the induction heating apparatus, which simultaneously unclamps the hub and inertia ring, and the damper may be directly placed within the shipping box or container wherein it cools to room temperature.
As the practice of the invention provides automatic unclamping and clamping of the hub and inertia ring while in the heating apparatus, these separate time-consuming steps are eliminated. Also, the practice of the invention, as compared to the previous steps of manufacture as described above, eliminates the second eccentricity gaging operation, and as cooling takes place after the damper has been boxed, and no operations are further required to the damper after heating, it is not necessary to wait for cooling to be achieved before further processing the dampers.
As compared with the prior system of assembling vibration dampers the practice of the invention concentrates the location of damper heating which requires less time per damper, utilizes less energy, and reduces the heating exposure of the elastomer minimizing the deleterious effects of the heat upon the elastomer.